Background The effects and analgesic adequacy of intrathecal morphine (ITM) administration have been studied less frequently than other regional analgesia techniques in pediatric surgical procedures. Objective To evaluate the efficacy and adverse event rate of 5 mu g/kg ITM administration for postoperative analgesia according to age group. Methods We retrospectively evaluated the medical records of patients who underwent major pediatric surgery and were administered ITM for postoperative analgesia. Patients were divided into three age groups: <= 5 years (group I), 5.1-13 years (group II) and > 13 years (group III). All patients received ITM 5 mu g/kg (max 300 mu g) through the L4-5 or L-5-S-1 interspace. Postoperative pain (modified pediatric objective pain score > 4), need for rescue analgesics, sleep interruption due to pain, sedation (Ramsay sedation scale score > 3), opioid-related postoperative adverse events (at 0, 4, 8, 12, and 24 h after intervention), hemodynamic data and nurse satisfaction with the analgesic method were compared between groups. Results The analysis included 100 children (47 girls, 9 +/- 5.4 years). Groups were similar regarding postoperative rescue analgesia consumption and sleep interruption (p = 0.238, p = 0.958), 96% of the children did not require rescue analgesia, and sleep interruption was not observed in 97%. Postoperative adverse events were pruritus in 14 and nausea/vomiting in 9 patients (p = 0.052). Overall, nurses were satisfied or very satisfied in 99% of the cases. Conclusion Administration of 5 mu g/kg ITM can be used for postoperative analgesia in pediatric surgery in all age groups, with no severe adverse events and high nurse satisfaction with analgesic management.